Combustion synthesis of glass (Al2O3-CaO-X-Y) ceramic (TiB2) composites

ABSTRACT

The present invention is directed to the preparation of in-situ formation of a series of glass-ceramic composites by the Self-propagating High temperature Synthesis (SHS) technique with advantages of processing simplicity as well as the potential of cost savings. The materials produced by the technique contain crystalline TiB 2  phase and have either a pure glassy matrix or a glass matrix with partial devitrification based on the Al 2 O 3 —CaO system. The materials can potentially be used for infrared light transmission and for other high temperature applications. These materials can also be produced with relatively high porosity.

CROSS REFERENCE

This application is a continuation-in-part of application Ser. No.09/591,902, filed Jun. 12, 2000 now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to the field of glass/ceramic compositesand more particularly to glasses based on Al₂O₃—CaO which include TiB₂phase.

It has long been found that alumininate glasses based on Al₂O₃ and CaOtransmit infra-red light. Although there are other glasses which dothis, (e.g., tellurites, germanates, etc.), the aluminates have a bettercombination of properties (optical, mechanical and thermal) as well aslower cost which makes them the attractive candidates when transmissionout to about 6 μ is required. Glasses based on CaO—Al₂O₃ may be goodcandidates for this type of application since they are infrared lighttransmittable, have high softening temperature (>1000° C.) and goodmechanical and thermal properties, and have lower costs compared toother similar materials Unfortunately, the CaO—Al₂O₃ system is readilydevitrified and requires high critical cooling rate in order to formstable glass.

To promote glass formation, silica (SiO₂) has been added with somesuccess. For instance, a composition of 48.6Al₂O₃-44.8CaO-6.6 SiO₂ (wt.%) was found to be devitrification free [see, J. E. Stanworth,, J. Soc.Glass Technol., 1948, vol. 32, pp. 154-172]. Glasses based on Al₂O₃-CaOwithout silica but with a complex composition were also produced [see,K. H. Sun, Glass Ind., 1949, vol. 30(4), pp.199-200, 232.]. Later on,silica free glasses with much simpler composition [e.g.,47Al₂O₃-43CaO-10BaO (wt. %)] were reported to be formed by Florence etal. [see, J. M., Florence, et al., J. Res. Natn. Bur. Stand., 1955, vol.55, pp.231-237]. Finally, many glass compositions based on Al₂O₃-CaO andcontaining Na₂O, K₂O, MgO, BaO, La₂O₃ and Fe₂O₃ were produced by Hafneret al. [H. C. Hafner et al., J. Am Ceramic Soc., vol 41(8), 1958,pp.315-323]. However, these glasses were also devitrified to a differentdegree and pure glasses were obtained only after up to 5 mol % SiO₂ wasadded.

This invention uses a novel technique to produce glasses based onAl₂O₃-CaO with the possibility of lower costs than the traditionalprocessing technique. The new glasses created in this invention have asimpler composition than those produced by Hafner et al. mentionedabove. The glass matrix is based on Al₂O₃-CaO-BaO-SiO₂ which containshigher A₂O₃ content and exhibits high softening temperature and bettercorrosion resistance. It also contains crystalline TiB₂ phase whichappears as precipitates. The material can also be produced to containrelatively high porosity which finds use in applications requiring lightweight and high temperature corrosion resistance.

The traditional technique of manufacturing Al₂O₃—CaO glasses involvesfusion of the oxides at 1400-1500° C. for a long time followed bycasting and shaping to desired shapes. On the other hand, this inventionuses the Self-propagating High Temperature Synthesis (SHS) or CombustionSynthesis technique which is a favorable technique to produce glassymaterials since the technique offers instant high combustion temperaturewithout a furnace.

The application of the SHS technique to produce various crystallinematerials has been demonstrated in many published articles and in anumber of review articles [e.g., Moore and Feng, Progress in MaterialsScience, Vol. 39, 243-316 (1995); Munir and Anselmi-Tamburini, MaterialsScience Reports, vol.3, 277-365 (1989), Yi and Moore, J. Mater. Sci.,vol. 25, 1159-1168 (1990)]. Simply speaking, the technique uses reactantpowders to form a green pellet which is then ignited by an external heatsource to generate chemical reactions, producing the end productin-situ. The SHS process can be realized by two modes, i.e., propagation(or combustion) mode and simultaneous (or thermal explosion) combustionmode. In the propagation mode, the reactants are ignited by an externalheat source. Once ignited, the highly exothermic reaction ignites thenext adjacent reactant layer by itself thereby generating aself-sustaining wave propagating toward the un-reacted part. In thesimultaneous combustion mode, all the reactants are heated uniformlyuntil the combustion reaction is initiated simultaneously throughout thewhole pellet. A combustion synthesis reaction is defined by mainly threeparameters: ignition temperature, which is the temperature at which thereaction rate becomes appreciable and self-sustaining; combustiontemperature, which is the maximum temperature achieved; and combustionwave velocity, which is the overall combustion rate. However, the stateof green reactants, (i.e. particle size, green density, reactionenvironment etc.) has a profound influence on the combustion synthesisprocess.

The present authors synthesized series of glass ceramic composites basedon Al₂O₃—B₂O₃—BaO and Al₂O₃—B₂O₃—MgO glasses using the SHS technique(see Yi et al, U.S. Pat. No. 5,792,417 and Yi et al., U.S. Pat.application Ser. No. 09/351,227). The present invention is a furthercontinuation in this work which reveals processing of another series ofglass-ceramic composites based on CaO—Al₂O₃—X—Y. In these series X and Ycan be any metal or any metal oxide. For purposes of this application,metal is defined to include Si. However in this document only examplesof X and Y being SiO₂ and BaO are given.

Development of glass (Al₂O₃—CaO—X—Y) ceramic (TiB₂) composites andmethods of synthesizing them represents a great improvement in the fieldof glasses and ceramics and satisfies a long felt need of the ceramicengineer.

SUMMARY OF THE INVENTION

This invention is a method for synthesising glass-ceramic composites,comprising the following steps:

1. mixing the reactant powders in proportion according to one of thefollowing reactions:

3TiO₂+3B₂O₃+10Al+αCaO→3TiB₂+5Al₂O₃+αCaO+Q  (1)

3TiO₂+3B₂O₃+10Al+αCaO+βX→3TiB₂+5Al₂O₃+αCaO+βX+Q  (2)

3TiO₂+3B₂O₃10Al+αCaO+βX+γY→3TiB₂5Al₂O₃+αCaO+βX+γY+Q  (3)

TiH₂+B₂O₃+2Al+αCaO+βX+γY→TiB₂+Al₂O₃+αCaO+βX+γY+H₂(g)+Q  (4)

Ti+B₂O₃+2Al+αCaO+βX+γY→TiB₂+Al₂O₃αCaO+βX+γY+Q  (5)

where X and Y represent any metal oxide or any metal. For the purposesof this application metal is defined to include Si. It is desirable tolimit the amount of silica to be added since it reduces the infraredtransmission and heavier oxide such as BaO is preferred.

2. pressing the mixed powders into pellets; and

3. igniting the pellets in an argon atmosphere by resistant heating of aW-wire.

The glasses or partially devitrified glasses produced are based on theA₂O₃—CaO system and may contain one or more other substances resultingin A₂O₃—CaO—X—Y. The preferred composition of the products isAl₂O₃—CaO—BaO—SiO₂. The products also contain a ceramic phase, theceramic phase being TiB₂. The preferred product has the followingcomposition:

TiB₂: 13-26 wt. %

Al₂O₃: 29-50 wt. %

CaO: 16-42 wt. %

SiO₂: 0-35 wt. %

BaO: 0-17 wt. %.

An appreciation of the other aims and objectives of the presentinvention and an understanding of it may be achieved by referring to theaccompanying drawings and description of a preferred embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of a typical temperature profile obtained duringcombustion synthesis of a sample having the composition50Al₂O₃-30CaO-10SiO-10BaO.

FIG. 2 is a graph illustrating the effect of Al₂O₃ content on combustioncharacteristics.

FIG. 3 is a graph illustrating the effect of diluent content oncombustion characteristics.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention uses powder reactants as raw materials. Thepowders are weighed according to the desired composition and thoroughlymixed by ball milling. Pellets with green densities (typically around60% of theoretical) are pressed uniaxially. The final products weresynthesized by igniting green pellets, thus establishing aself-propagating combustion reaction until the whole pellet is reacted.The combustion reactions were ignited by the propagation combustionmode. Pellets were ignited at one end in an inert atmosphere inside achamber, and the combustion proceeded in a self-propagating way. Thecombustion temperatures (Tc) were measured by inserting C-type (5% W-Rhvs 26% W-Rh) thermocouples and wave velocities were measured byframe-by-frame analysis of a video recording of the combustion reaction.Microstructures were analysed by X-ray diffraction (XRD) and microscope.

Pellets could also be ignited by the simultaneous combustion mode, wherea pellet was placed inside a furnace and heated to a certain temperatureuntil combustion reactions are generated throughout of the whole sample.Combustion synthesis operations could also be carried out in air usingother ignition techniques shown in our previous work (Yi et al., U.S.patent in application Ser. No. 09/351,227).

Binary CaO—Al₂O₃ with different compositions were first synthesizedaccording to the following reaction:

3TiO₂+3B₂O₃+10Al++αCaO→3TiB₂+5Al₂O₃+αCaO+Q  (1)

The self-propagating combustion reaction is sustained by aluminumreducing TiO₂ and B₂O₃ at the combustion front thus releasing a largeamount of heat (Q=612.4 kilo calorie) which is high enough to fuse theAl₂O₃ and CaO together forming a matrix comprising the two phases. Thecrystalline TiB₂ phase also exists in the product as a by-product(throughout document, the term matrix refers to the phases excluding theTiB₂ phase). By adjusting the coefficient a, binary CaO—Al₂O₃ systemwith different matrix compositions can be created. In the current work,compositions with different mass ratios of the two oxides were produced,with those containing higher aluminum oxide having higher combustiontemperatures and wave velocities as expected. Unfortunately, none ofthese binary compositions formed pure glass matrices as will be shownlater.

As mentioned before, glass formation may be promoted by adding anotherglass former such as SiO₂, or by adding another substance like BaO, orby adding both or more. To achieve this, the following reactions wereconducted:

3TiO₂+3B₂O₃+10Al+αCaO+βX→3TiB₂+5Al₂O₃+αCaO+βX+Q  (2)

3TiO₂+3B₂O₃+10Al+αCaO+βX+γY→3TiB₂+5Al₂O₃+αCaOβX+γY+Q  (3)

X and Y can be any metal or metal oxide. For purposes of thisapplication, metal is defined to include Si. In reaction (2), X (e.g.,SiO₂, or BaO) is added to promote and stabilize the glass melt, while inreaction (3), both X (e.g., SiO₂) and Y (e.g., BaO) are added. Therelative amounts of oxides in the glass matrix are adjusted by thecoefficients α, β, and γ. Like CaO, the substances represented by X andY act as diluents which reduce the combustion temperature and wavevelocity. Therefore, there are maximum amounts of diluents that can beadded without affecting self-propagating combustion reactions.

It was found that the combustion characteristics are greatly affected bythe amount of diluent and by the amount of aluminium in the startingmaterials. Both the combustion temperature and wave velocity decreasedwith the increase of the amounts of diluents, and the opposite is trueas the amount of aluminium oxide is increased. The latter was apparentlycaused by the increased exothermicity.

Microstructural analysis showed that none of the materials produced byreaction (1) formed substantial glass phase. However, those produced byreaction (2), i.e., Al₂O₃—CaO—SiO₂ system do form glass. As the amountof the SiO₂ increased, the glass phase also increased. It was also foundthat samples containing higher aluminum oxide favor glass formation,possibly due to higher combustion temperature associated with thesecombustion reactions. The combination of SiO₂ and BaO, as prepared byconducting reaction (3), also promoted glass formation. Materials withpure glass matrices have been formed in this system. All materials alsocontain the TiB₂ phase.

Typical apparent porosity (open pores) of the reacted samples was around<30% and overall porosity around 60% when samples were prepared usingtitanium dioxide as one of the reactants. In an effort to make thesematerials more porous, titanium hydride (TiH₂) was substituted for thetitanium dioxide (TiO₂). For example, to produce porousAl₂O₃—CaO—SiO₂—BaO glass, the following reaction was carried out:

TiH₂+B₂O₃+2AlαCaO+βXγY→TiB₂+Al₂O₃+αCaO+βX+γY+H₂(g)+Q  (4)

The evolution of the hydrogen gas at the combustion front promotedformation of pores. The final reacted products contained apparentporosity of >40% and overall porosity of 60%. Exactly the same productscan also be formed by substituting titanium dioxide in Reactions (1)-(3)by titanium. For instance, the glass matrix of Al₂O₃—CaO—SiO₂—BaO canalso be produced by the following reaction:

Ti+B₂O₃+2Al+αCaO+βX+γY→TiB₂+Al₂O₃αCaO+βXγY+Q  (5)

Materials

Characteristics of the reaction powders are listed in Table 1.

TABLE I Specifications of the Reactant Powders Reactant Particle Size,μm Impurity, % Al <44 <0.5 B₂O₃ <44 <0.02 CaO <44 <0.01 SiO₂ <44 <0.5TiH₂ <44 <1 BaO <149 <0.5 Ti <44 <1

Examples of various matrix compositions in reacted products and thefractions of reactants to form them are given in Tables 2 and 3. Thecompositions are represented by weight (mass) percentage throughout thisdocument unless specified otherwise. The matrix composition here isdefined as the composition of the reacted product excluding TiB₂. Forexample, a composition represented by 50A₂O₃-30CaO-10SiO₂ -10BaO meansthe composition excluding TiB2 is 50wt. % Al₂O₃ -30wt. % CaO-10wt. %SiO₂ -10 wt. % BaO. The overall composition (including TiB₂ phase) ofthese materials is shown in Table 4.

Materials shown in Table 2 used TiO₂ as one of the reactants. However,in certain situations, porous glass materials may be desired. Therefore,titanium hydride (TiH₂) was used to replace titanium oxide to generatethe same materials shown in the Table 2. Examples of selected materialswith the same matrix composition are shown in Table 3. These materialsproduced using titanium hydride instead of titanium oxide contain higherporosity due to the evolution of hydrogen gas at the combustion front asshown in reaction (4).

TABLE 2 Matrix Compositions (wt. %) of selected samples produced by theCombustion Reactions (1)-(3) and the weight percentage of Reactants toproduce them Matrix Composition in Product (wt. %) alpha beta gamma TiO₂B₂O₃ Al CaO SiO₂ BaO Reaction 50Al₂O₃-50CaO 9.1 0.0 0.0 19.5 17.0 22.041.5 0.0 0.0 1 45Al₂O₃-45CaO-10SiO₂ 9.1 1.9 0.0 17.9 15.6 20.1 38.0 8.40.0 2 40Al₂O₃-40CaO-20SiO₂ 9.1 4.2 0.0 16.2 14.1 18.2 34.4 17.2 0.0 240Al₂O₃-40CaO-10SiO₂-10BaO 9.1 2.1 0.8 16.2 14.1 18.2 34.4 8.6 8.6 347Al₂O₃-43CaO-10BaO 8.3 0.0 0.7 18.5 16.2 20.8 36.1 0.0 8.4 245Al₂O₃-35CaO-20SiO₂ 7.1 3.8 0.0 17.9 15.6 20.1 29.6 16.9 0.0 239.4Al₂O₃-30.6CaO-30SiO₂ 7.1 6.5 0.0 15.9 13.9 17.9 26.4 25.8 0.0 245Al₂O₃-35CaO-10SiO₂-10BaO 7.1 1.9 0.7 17.9 15.6 20.1 29.6 8.4 8.4 362.5Al₂O₃-37.5CaO 5.5 0 0 23.4 20.4 26.3 29.9 0.0 0.0 156.25Al₂O₃-33.75CaO-10SiO₂ 5.5 1.5 0.0 21.5 18.7 24.2 27.4 8.1 0.0 350Al₂O₃-30CaO-20SiO₂ 5.5 3.4 0.0 19.5 17.0 22.0 24.9 16.6 0.0 243.8Al₂O₃-26.2CaO-30SiO₂ 5.5 5.8 0.0 17.4 15.2 19.6 22.3 25.4 0.0 237.5Al₂O₃-22.5CaO-40SiO₂ 5.5 9.0 0.0 15.3 13.3 17.2 19.5 34.7 0.0 250Al₂O₃-30CaO-20BaO 5.5 0.0 1.3 19.5 17.0 22.0 24.9 0.0 16.6 250Al₂O₃-30CaO-5SiO₂-15BaO 5.5 0.8 1.0 19.5 17.0 22.0 24.9 4.2 12.5 350Al₂O₃-30CaO-10SiO₂-10BaO 5.5 1.7 0.7 19.5 17.0 22.0 24.9 8.3 8.3 350Al₂O₃-30CaO-15SiO₂-5BaO 5.5 2.5 0.3 19.5 17.0 22.0 24.9 12.5 4.2 350Al₂O₃-30CaO-17.5SiO₂-2.5BaO 5.5 3.0 0.2 19.5 17.0 22.0 24.9 14.5 2.1 345Al₂O₃-27CaO-20SiO₂-8BaO 5.5 3.8 0.6 17.9 15.6 20.1 22.8 16.9 6.8 341.7Al₂O₃-25CaO-20SiO₂-13.3BaO 5.4 4.1 1.1 16.7 14.6 18.9 21.4 17.1 11.43

TABLE 3 Matrix Compositions (wt. %) of selected samples produced by theCombustion Reactions (4) and the weight percentage of reactants toproduce them Matrix Composition in Product (wt. %) alpha beta gammaTiH₂/Ti B₂O₃ Al CaO SiO₂ BaO Reaction 50Al₂O₃-30CaO-10SiO₂-10BaO 1.1 0.30.1 18.1 25.3 19.6 22.2 7.4 7.4 4 50Al₂O₃-30CaO-15SiO₂-5BaO 1.1 0.5 0.118.1 25.3 19.6 22.2 11.1 3.7 4 50Al₂O₃-30CaO-17.5SiO₂-2.5BaO 1.1 0.6 0.018.1 25.3 19.6 22.2 13.0 1.9 4 33.3Al₂O₃-20CaO-30SiO₂-16.7Ba0 1.1 1.50.3 13.2 18.4 14.3 16.2 24.3 13.5 4 37.5Al₂O₃-22.5CaO-40SiO₂ 1.1 1.8 0.014.5 20.3 15.7 17.8 31.7 0.0 4 50Al₂O₃-30CaO-10SiO₂-10BaO 1.1 0.3 0.117.5 25.5 19.7 22.4 7.5 7.5 5 50Al₂O₃-30CaO-15SiO₂-5BaO 1.1 0.5 0.1 17.525.5 19.7 22.4 11.2 3.7 5 50Al₂O₃-30CaO-17.5SiO₂-2.5BaO 1.1 0.6 0.0 17.525.5 19.7 22.4 13.1 1.9 5

TABLE 4 Overall Compositions (wt. %) of selected samples produced by theReactions (1)-(4) Matrix Composition in Product (wt. %) TiB₂ Al₂O₃ CaOSiO₂ BaO Reaction 50Al₂O₃-50CaO 17.0 41.5 41.5 0.0 0.0 145Al₂O₃-45CaO-10SiO₂ 15.5 38.0 38.0 8.4 0.0 2 40Al₂O₃-40CaO-20SiO₂ 14.134.4 34.4 17.2 0.0 2 40Al₂O₃-40CaO-10SiO₂-10BaO 14.1 34.4 34.4 8.6 8.6 347Al₂O₃-43CaO-10BaO 16.1 39.4 36.1 0.0 8.4 2 45Al₂O₃-35CaO-20SiO₂ 15.538.0 29.6 16.9 0.0 2 39.4Al₂O₃-30.6CaO-30SiO₂ 13.9 33.9 26.4 25.8 0.0 245Al₂O₃-35CaO-10SiO₂-10BaO 15.5 38.0 29.6 8.4 8.4 3 62.5Al₂O₃-37.5CaO20.4 49.8 29.9 0.0 0.0 1 56.25Al₂O₃-33.75CaO-10SiO₂ 18.7 45.7 27.4 8.10.0 2 50Al₂O₃-30CaO-20SiO₂ 17.0 41.5 24.9 16.6 0.0 243.8Al₂O₃-26.2CaO-30SiO₂ 15.2 37.1 22.3 25.4 0.0 237.5Al₂O₃-22.5CaO-40SiO₂ 13.3 32.5 19.5 34.7 0.0 2 50Al₂O₃-30CaO-20BaO17.0 41.5 24.9 0.0 16.6 2 50Al₂O₃-30CaO-5SiO₂-15BaO 17.0 41.5 24.9 4.212.5 3 50Al₂O₃-30CaO-10SiO₂-10BaO 17.0 41.5 24.9 8.3 8.3 350Al₂O₃-30CaO-15SiO₂-5BaO 17.0 41.5 24.9 12.5 4.2 350Al₂O₃-30CaO-17.5SiO₂-2.5BaO 17.0 41.5 24.9 14.5 2.1 345Al₂O₃-27CaO-20SiO₂-8BaO 15.5 38.0 22.8 16.9 6.8 341.7Al₂O₃-25CaO-20SiO₂-13.3BaO 14.6 35.6 21.4 17.1 11.4 350Al₂O₃-30CaO-10SiO₂-10BaO 25.4 37.3 22.4 7.5 7.5 450Al₂O₃-30CaO-15SiO₂-5BaO 25.4 37.3 22.4 11.2 3.7 450Al₂O₃-30CaO-17.5SiO₂-2.5BaO 25.4 37.3 22.4 13.1 1.9 450Al₂O₃-30CaO-10SiO₂-10BaO 25.4 37.3 22.4 7.5 7.5 550Al₂O₃-30CaO-15SiO₂-5BaO 25.4 37.3 22.4 11.1 3.7 550Al₂O₃-30CaO-17.5SiO₂-2.5BaO 25.4 37.3 22.4 13.1 1.9 5

Experimental Procedures

Preparation started by weighing the reactant powders according to thedesired compositions and thoroughly mixing them using ball milling dryin an inert atmosphere for at least 12 hours. Green pellets were thenprepared by pressing the mixed powders uniaxially into density ofapproximately 60% of their theoretical densities. Green pellets wereignited by resistant heating a W-coil in an inert atmosphere inside areaction chamber.

Ignition of the combustion reactions were realized by using an Xantrexpower supply (model no XFR40-70, available from Xantrex Technology, Inc.of Burnaby, BC, Canada). The ignition power was controlled by computerand kept constant at 20V, 69A, 3 seconds for all of the samples.Temperature profiles during the combustion reactions were recorded by adata acquisition system using the DAQPad-1200 from National InstrumentsCorporation of Austin, Tex. Two C-type thermocouples (W-5% Re/W-26% Re)of 0.005 inches in diameter (welded under flowing argon atmosphere) wereused. The thermocouple signals were conditioned and amplified by 5Bseries modules which were also from National Instruments. Finally, avideo recording system consisting of a color camera with micro-zoom lensand a VCR was used to record the whole combustion process, from whichthe wave velocity was determined by frame-by-frame analysis of the wavefront.

Combustion Characteristics

The ignition of these pellets was fairly easy and a self-propagatingcombustion wave was established in all samples. A typical temperatureprofile for a matrix composition of 50A₂O₃-30CaO-10SiO₂-10BaO (wt. %)that formed pure glass matrix (using reaction (3)) is shown in FIG. 1.The curve can be divided into three portions. The first portion (I)represents the temperature of the un-reacted part (room temperature),and the second portion (II) represents the sudden temperature rise tothe maximum (combustion Temperature, Tc) when the combustion wave passedthrough the location of the thermocouples. A glass melt is formed at thecombustion front. The third portion (III) represents the cooling processof the glass melt.

The relative amount of aluminum oxide, R (defined as the ratio of masspercentage of Al₂O₃ to that of CaO) in the matrix affects combustioncharacteristics substantially. This is illustrated in FIG. 2, where boththe combustion temperature and wave velocity are plotted versus R forsamples containing 20 wt. % SiO₂. The combustion temperatures increasedfrom 1724 to 1919K, while the wave velocity increased from 1.1 to 3.1mm/sec, as the R increased from 1.0 to 1.67 due to more heat beingreleased. Undoubtedly, glass formation is also influenced substantiallyby combustion characteristics, particularly by the combustiontemperature.

The combustion characteristics are also affected by the amount ofdiluents, as plotted in FIG. 3 for samples reacted for reaction (2). Inthis plot, the R value is kept constant at 1.67. The combustiontemperature decreased from 2069K to 1773K while the wave velocitydecreased from 4.1 mm/sec to 0.7 mm/sec, as the amount of silicaincreased from 0 to 40 wt. %.

As mentioned earlier, titanium hydride (TiH₂) can be used to substitutefor titanium oxide (TiO₂) to produce exactly the same compositions usingreaction (4). It was found that for the same composition produced usingreaction (4), both the combustion temperatures and wave velocities werelower than these produced using reaction (3). Titanium (Ti) can also beused to substitute titanium oxide (TiO₂) to produce the same usingreaction (5).

Combustion characteristics of selected compositions for all of the fivereactions are summarized in Tables 5 and 6.

TABLE 5 Combustion Temperature and Wave Velocity (average) for samples(represented by matrix composition) produced by Reactions (1)-(3) V,Matrix Composition (wt. %) Tc, K mm/s R Reaction 50 Al₂O₃-50 CaO 21084.1 1 1 45 Al₂O₃-45 CaO-10 SiO₂ 1706 1.7 1 2 40 Al₂O₃-40 CaO-20 SiO₂1724 0.96 1 2 40 Al₂O₃-40 CaO-10 SiO₂-10 BaO 1782 0.78 1 3 47 Al₂O₃-43CaO-10 BaO 2013 2.2 1.09 2 45 Al₂O₃-35 CaO-20 SiO₂ 1847 2.2 1.29 2 39.4Al₂O₃-30.6 CaO-30 SiO₂ 1809 0.9 1.29 2 45 Al₂O₃-35 CaO-10 SiO₂-10 BaO1978 3.7 1.29 3 62.5 Al₂O₃-37.5 CaO 2069 4.1 1.67 1 56.25 Al₂O₃-33.75CaO-10 SiO₂ 1870 3.7 1.67 2 50 Al₂O₃-30 CaO-20 SiO₂ 1944 3.1 1.67 2 43.8Al₂O₃-26.2 CaO-30 SiO₂ 1850 1.3 1.67 2 37.5 Al₂O₃-22.5 CaO-40 SiO₂ 17730.7 1.67 2 50 Al₂O₃-30 CaO-20 BaO 2040 0.36 1.67 2 50 Al₂O₃-30 CaO-5SiO₂-15 BaO 1958 0.32 1.67 3 50 Al₂O₃-30 CaO-10 SiO₂-10 BaO 1912 2.81.67 3 50 Al₂O₃-30 CaO-15 SiO₂-5 BaO 1950 1.6 1.67 3 50 Al₂O₃-30CaO-17.5 SiO₂-2.5 BaO 1806 1.9 1.67 3 45 Al₂O₃-27 CaO-20 SiO₂-8 BaO 19162.1 1.67 3 41 Al₂O₃-25 CaO-20 SiO₂-13 BaO 1875 1.7 1.67 3

TABLE 6 Combustion Temperature and Wave Velocity (average) for sample(represented by matrix composition) produced by Reactions (1)-(3) V,Matrix Composition in Product (wt. %) Tc, K mm/s R Reaction 50 Al₂O₃-30CaO-10 SiO₂-10 BaO 1959 1.8 1.67 4 50 Al₂O₃-30 CaO-15 SiO₂-5 BaO 18711.2 1.67 4 50 Al₂O₃-30 CaO-17.5 SiO₂-2.5 BaO 1602 1.5 1.67 4 2324 50Al₂O₃-30 CaO-10 SiO₂-10 BaO 5.2 1.67 5 50 Al₂O₃-30 CaO-15 SiO₂-5 BaO2229 4.8 1.67 5 50 Al₂O₃-30 CaO-17.5 SiO₂-2.5 BaO 2258 5.2 1.67 5

Glass Formation

The XRD and microscopic analysis results carried out are summarized inTable 7. The conventions used to describe the matrices in Table 7 are:pure glass indicating neither observable crystalline peaks on XRDpatterns nor under microscope; mainly glass indicating small crystallinepeaks on XRD patterns and/or small size sporadic crystalline phasesobserved under microscope; devitrified indicating appreciable amount ofcrystalline phases on the XRD and observable crystals in the glassmatrix under microscope; and totally devitrified indicating mainlycrystalline peaks on XRD and under microscope. All samples contain TiB2phase which appears as crystalline precipitates.

Although the binary Al₂O₃—CaO system (near R=1) is a glass former [seeH. Rawson, “inorganic glass-forming systems”, Academic Press, London andNew York (1967)], the present work on two compositions, i.e.,50Al₂O₃-5CaO, 62.5Al₂O₃-37.5CaO showed that they do not form glasses atall. Full devitrification occurred throughout these samples most likelydue to the fact that these compositions require a very high criticalcooling rate to form glass.

In order to promote glass formation, different amounts of SiO₂ werefirst added to the Al₂O₃—CaO system while keeping the R value at 1. Upto 20% of SiO₂ was added, but no pure glass matrix was formed.Examination of an optical photomicrograph of a samples with a matrixcomposition of 45Al₂O₃-45CaO-10SiO₂ revealed that extensivedevitrification had occurred in the glass matrix. However, as the amountof silica increases, less devitrification and more glass phase had beenformed. This was clear from examination of a photomicrograph of a samplewith a matrix composition of 40Al₂O₃-40CaO-20SiO₂. Therefore, it can beconcluded that silica indeed promotes glass formation.

Next, the R value was increased to 1.29 and up to 30% SiO₂ was added.Both the combustion temperature and wave velocity were increasedcompared to the samples with an R value of 1 and the same amount ofsilica (see FIG. 2). More importantly, it was found that more glassphases were formed. For instance, the samples containing more than 20%SiO₂ formed a mainly glass matrix (matrix composition of45Al₂O₃-35CaO-20SiO₂ and of 39.4Al₂O₃-30.6CaO-30SiO₂). Comparing anoptical photomicrograph of the 45Al₂O₃-35CaO-20SiO₂ with opticalphotomicrographs of other compositions, one concludes that morealuminium oxide also promotes glass formation, possibly through raisingof the combustion temperature.

Further raising the R value to 1.67 had similar results to that with theR value being 1.29. In this case, samples with 10% SiO₂ added(56.25Al₂O₃-33.75CaO-10SiO₂) formed pure glass matrices. However othercrystalline phases other than the TiB₂ were also observed on XRD.Increasing the silica concentration to 20% (50Al₂O₃-30CaO-20SiO₂)resulted in a mainly glass matrix. However, as the amount of silicafurther increased to 30%(43.8Al₂O₃-26.2CaO-30SiO₂) and 40%(37.5Al₂O₃-22.5CaO-40SiO₂), even more devitrification occurred. Apossible reason for this is that the combustion temperatures became toolow.

In a work reported by Florence et al., a silica free sample with thecomposition of 47Al₂O₃-43CaO-10BaO was found to have formed glass. Thiswork seems to suggest that BaO also promotes glass formation.Unfortunately, the samples with the same matrix composition done in thecurrent work failed to form pure glass (devitrification occurred). Thisis a composition that has a R value of 1.09 and the combustiontemperature was 2013K.

Further attempts were also made to partially replace silica with BaO.Samples with a matrix composition of 40Al₂O₃-40CaO-10SiO₂-10BaO (R=1)and of 45Al₂O₃-35CaO-10SiO₂-10BaO (R=1.29) still devitrified, but a pureglass matrix was obtained for samples with matrix compositionof50Al₂O₃-30CaO-10SiO₂-10BaO, 50Al₂O₃-30CaO-15SiO₂-5BaO,45Al₂O₃-27CaO-20SiO₂-8BaO, and 41Al₂O₃-25CaO-20SiO₂-13BaO (R=1.67). TiB₂is the only crystalline phase in these samples. On the other hand, thosesamples with silica free composition (e.g., 47Al₂O₃-43CaO-10BaO,50Al₂O₃-30CaO-20BaO) failed to produce pure glass matrices in thecurrent work. Therefore, it appears that both BaO and SiO₂ are requiredto stabilize Al₂O₃—CaO glass melts.

The vitrification behavior of samples produced from reactions (4) and(5), i.e., using titanium hydride or titanium to replace titaniumdioxide, were the same. For instance, the samples with a matrixcomposition of 50Al₂O₃-30CaO-10SiO₂-10BaO produced by both reaction alsoformed a pure glass matrix (see Table 7).

TABLE 7 Microstructures of Reacted Samples R Matrix Compositions (wt. %)Matrix Reaction 1 50 Al₂O₃-50 CaO Totally 1 Devitrified 1 45 Al₂O₃-45CaO-10 SiO₂ Devitrified 2 1 40 Al₂O₃-40 CaO-20 SiO₂ Devitrified 2 1 40Al₂O₃-40 CaO-10 SiO₂-10 BaO Devitrified 3 1.09 47 Al₂O₃-43 CaO-10 BaODevitrified 2 1.29 45 Al₂O₃-35 CaO-20 SiO₂ Mainly Glass 2 1.29 39.4Al₂O₃-30.6 CaO-30 SiO₂ Mainly Glass 2 1.29 45 Al₂O₃-35 CaO-10 SiO₂-10BaO Mainly Glass 3 1.67 62.5 Al₂O₃-37.5 CaO Totally 1 Devitrified 1.6756.25 Al₂O₃-33.75 CaO-10 SiO₂ Pure Glass^(†) 2 1.67 50 Al₂O₃-30 CaO-20SiO₂ Mainly Glass 2 1.67 43.8 Al₂O₃-26.2 CaO-30 SiO₂ Mainly Glass 2 1.6737.5 Al₂O₃-22.5 CaO-40 SiO₂ Devitrified 2 1.67 50 Al₂O₃-30 CaO-20 BaODevitrified 2 1.67 50 Al₂O₃-30 CaO-5 SiO₂-15 BaO Devitrified 3 1.67 50Al₂O₃-30 CaO-10 SiO₂-10 BaO Pure Glass 3 1.67 50 Al₂O₃-30 CaO-15 SiO₂-5BaO Pure Glass 3 1.67 50 Al₂O₃-30 CaO-17.5 SiO₂-2.5 BaO Mainly Glass 31.67 45 Al₂O₃-27 CaO-20 SiO₂-8 BaO Pure Glass 3 1.67 41.7 Al₂O₃-25CaO-20 SiO₂-13.3 BaO Pure Glass 3 1.67 50 Al₂O₃-30 CaO-10 Si₂-10 BaOPure Glass 4 1.67 50 Al₂O₃-30 CaO-15 SiO₂-5 BaO Pure Glass 4 1.67 50Al₂O₃-30 CaO-17.5 SiO₂-2.5 BaO Mainly Glass 4 1.67 50 Al₂O₃-30 CaO-10SiO₂-10 BaO Pure Glass 5 1.67 50 Al₂O₃-30 CaO-15 SiO₂-5 BaO Pure Glass 51.67 50 Al₂O₃-30 CaO-17.5 SiO₂-2.5 BaO Pure Glass 5 ^(†)Othercrystalline phases, other than TiB₂, were also observed on XRD.

The morphology of the TiB₂ phase was also examinedphotomicrographically.

Porosity of the Products

Measurements on porosity of the reacted samples by the Archimedes methodusing water revealed that the overall porosity was around 60% (Table 8).Samples produced using reaction (4) had higher open and interconnected(apparent) pores than those produced by reaction (3). This is clearlycaused by the evolution of the hydrogen gas generated in reaction (4).

TABLE 8 Porosity of Samples Apparent Porosity Samples (%) (%) 50Al₂O₃-30 CaO-10 SiO₂-10 BaO Reaction (3) 19 60 50 Al₂O₃-30 CaO-10SiO₂-10 BaO Reaction (4) 39 60 50 Al₂O₃-30 CaO-15 SiO₂-5 BaO Reaction(3) 11 62 50 Al₂O₃-30 CaO-15 SiO₂-5 BaO Reaction (4) 42 60

EXAMPLE 1

Reactant powders were dry mixed in proportions corresponding to a matrixcomposition of 50A₂O₃-50CaO for at least 12 hours using ball milling.Cylindrical pellets of 2.5 grams each were then pressed uniaxially to agreen density of 60% of theoretical. The pellets were then ignited in acombustion chamber by resistant heating a W-coil under inert Argonatmosphere. The average combustion temperature (Tc) was 2108 K and theaverage wave velocity was 4.1 mm/sec. X-ray diffraction (XRD) on powderscrushed from the reacted pellets and microscopic observation on polishedsamples showed that the matrix was composed of totally crystallinephases, in addition to the TiB₂ phase.

EXAMPLE 2

Reactant powders were dry mixed in proportions corresponding to a matrixcomposition of 45A₂O₃-45CaO-10SiO₂ for at least 12 hours using ballmilling. Cylindrical pellets of 2.5 grams each were then presseduniaxially to a green density of ˜60% of theoretical. The pellets werethen ignited in a combustion chamber by resistant heating a W-coil underinert Argon atmosphere. The average combustion temperature (Tc) was 1842K and the average wave velocity was 1.7 mm/sec. X-ray diffraction (XRD)on powders crushed from the reacted pellets and microscopic observationon polished samples showed that the matrix was composed of a mixture ofglass and crystalline phases, in addition to the TiB₂ phase.

EXAMPLE 3

Reactant powders were dry mixed in proportions corresponding to a matrixcomposition of 40A₂O₃-40CaO-20SiO₂ for at least 12 hours using ballmilling. Cylindrical pellets of 2.5 grams each were then presseduniaxially to a green density of ˜60% of theoretical. The pellets werethen ignited in a combustion chamber by resistant heating a W-coil underinert Argon atmosphere. The average combustion temperature (Tc) was 1724K and the average wave velocity was 1.1 mm/sec. X-ray diffraction (XRD)on powders crushed from the reacted pellets and microscopic observationon polished samples showed that the matrix was composed of a mixture ofglass and crystalline phases, in addition to the TiB₂ phase.

EXAMPLE 4

Reactant powders were dry mixed in proportions corresponding to a matrixcomposition of 40A₂O₃-40CaO-10SiO₂-10BaO for at least 12 hours usingball milling. Cylindrical pellets of 2.5 grams each were then presseduniaxially to a green density of ˜60% of theoretical. The pellets werethen ignited in a combustion chamber by resistant heating a W-coil underinert Argon atmosphere. The average combustion temperature (Tc) was 1739K and the average wave velocity was 1.5 mm/sec. X-ray diffraction (XRD)on powders crushed from the reacted pellets and microscopic observationon polished samples showed that the matrix was composed of a mixture ofglass and crystalline phases, in addition to the TiB₂ phase.

EXAMPLE 5

Reactant powders were dry mixed in proportions corresponding to a matrixcomposition of 47A₂O₃-43CaO-10BaO for at least 12 hours using ballmilling. Cylindrical pellets of 2.5 grams each were then presseduniaxially to a green density of ˜60% of theoretical. The pellets werethen ignited in a combustion chamber by resistant heating a W-coil underinert Argon atmosphere. The average combustion temperature (Tc) was 2013K and the average wave velocity was 2.2 mm/sec. X-ray diffraction (XRD)on powders crushed from the reacted pellets and microscopic observationon polished samples showed that the matrix was composed of devitrifiedglass phases, in addition to the TiB₂ phase.

EXAMPLE 6

Reactant powders were dry mixed in proportions corresponding to a matrixcomposition of 45A₂O₃-35CaO-20SiO₂ for at least 12 hours using ballmilling. Cylindrical pellets of 2.5 grams each were then presseduniaxially to a green density of ˜60% of theoretical. The pellets werethen ignited in a combustion chamber by resistant heating a W-coil underinert Argon atmosphere. The average combustion temperature (Tc) was 1847K and the average wave velocity was 2.2 mm/sec. X-ray diffraction (XRD)on powders crushed from the reacted pellets and microscopic observationon polished samples showed that the matrix was composed of mainly glassphase, in addition to the TiB₂ phase.

EXAMPLE 7

Reactant powders were dry mixed in proportions corresponding to a matrixcomposition of 39.4A₂O₃-30.6CaO-30SiO₂ for at least 12 hours using ballmilling. Cylindrical pellets of 2.5 grams each were then presseduniaxially to a green density of ˜60% of theoretical. The pellets werethen ignited in a combustion chamber by resistant heating a W-coil underinert Argon atmosphere. The average combustion temperature (Tc) was 1809K and the average wave velocity was 0.9 mm/sec. X-ray diffraction (XRD)on powders crushed from the reacted pellets and microscopic observationon polished samples showed that the matrix was composed of mainly glassphase, in addition to the TiB₂ phase.

EXAMPLE 8

Reactant powders were dry mixed in proportions corresponding to a matrixcomposition of 45A₂O₃-35CaO-10SiO₂-10BaO for at least 12 hours usingball milling. Cylindrical pellets of 2.5 grams each were then presseduniaxially to a green density of ˜60% of theoretical. The pellets werethen ignited in a combustion chamber by resistant heating a W-coil underinert Argon atmosphere. The average combustion temperature (Tc) was 1978K and the average wave velocity was 3.7 mm/sec. X-ray diffraction (XRD)on powders crushed from the reacted pellets and microscopic observationon polished samples showed that the matrix was composed of mainly glassphase, in addition to the TiB₂ phase.

EXAMPLE 9

Reactant powders were dry mixed in proportions corresponding to a matrixcomposition of 62.5A₂O₃-37.5CaO for at least 12 hours using ballmilling. Cylindrical pellets of 2.5 grams each were then presseduniaxially to a green density of ˜60% of theoretical. The pellets werethen ignited in a combustion chamber by resistant heating a W-coil underinert Argon atmosphere. The average combustion temperature (Tc) was 2069K and the average wave velocity was 4.1 mm/sec. X-ray diffraction (XRD)on powders crushed from the reacted pellets and microscopic observationon polished samples showed that the matrix was composed of totallycrystalline phases, in addition to the TiB₂ phase.

EXAMPLE 10

Reactant powders were dry mixed in proportions corresponding to a matrixcomposition of 56.25A₂O₃-33.75CaO-10SiO₂ for at least 12 hours usingball milling. Cylindrical pellets of 2.5 grams each were then presseduniaxially to a green density of ˜60% of theoretical. The pellets werethen ignited in a combustion chamber by resistant heating a W-coil underinert Argon atmosphere. The average combustion temperature (Tc) was 1919K and the average wave velocity was 3.7 mm/sec. X-ray diffraction (XRD)on powders crushed from the reacted pellets and microscopic observationon polished samples showed that the matrix was composed of pure glass,in addition to the TiB₂ phase, and other unknown crystalline phases.

EXAMPLE 11

Reactant powders were dry mixed in proportions corresponding to a matrixcomposition of 50A₂O₃-30CaO-20SiO₂ for at least 12 hours using ballmilling. Cylindrical pellets of 2.5 grams each were then presseduniaxially to a green density of ˜60% of theoretical. The pellets werethen ignited in a combustion chamber by resistant heating a W-coil underinert Argon atmosphere. The average combustion temperature (Tc) was 1944K and the average wave velocity was 3.1 mm/sec. X-ray diffraction (XRD)on powders crushed from the reacted pellets and microscopic observationon polished samples showed that the matrix was composed of mainly glassphase, in addition to the TiB₂ phase.

EXAMPLE 12

Reactant powders were dry mixed in proportions corresponding to a matrixcomposition of 43.8A₂O₃-26.2CaO-30SiO₂ for at least 12 hours using ballmilling. Cylindrical pellets of 2.5 grams each were then presseduniaxially to a green density of 60% of theoretical. The pellets werethen ignited in a combustion chamber by resistant heating a W-coil underinert Argon atmosphere. The average combustion temperature (Tc) was 1850K and the average wave velocity was 1.3 mm/sec. X-ray diffraction (XRD)on powders crushed from the reacted pellets and microscopic observationon polished samples showed that the matrix was composed of mainly glassphase, in addition to the TiB₂ phase.

EXAMPLE 13

Reactant powders were dry mixed in proportions corresponding to a matrixcomposition of 37.5A₂O₃-22.5CaO-20SiO₂ for at least 12 hours using ballmilling. Cylindrical pellets of 2.5 grams each were then presseduniaxially to a green density of ˜60% of theoretical. The pellets werethen ignited in a combustion chamber by resistant heating a W-coil underinert Argon atmosphere. The average combustion temperature (Tc) was 1773K and the average wave velocity was 0.7 mm/sec. X-ray diffraction (XRD)on powders crushed from the reacted pellets and microscopic observationon polished samples showed that the matrix was composed of a mixture ofglass and crystalline phases, in addition to the TiB₂ phase.

EXAMPLE 14

Reactant powders were dry mixed in proportions corresponding to a matrixcomposition of 50A₂O₃-30CaO-20BaO for at least 12 hours using ballmilling. Cylindrical pellets of 2.5 grams each were then presseduniaxially to a green density of ˜60% of theoretical. The pellets werethen ignited in a combustion chamber by resistant heating a W-coil underinert Argon atmosphere. The average combustion temperature (Tc) was2040K and the average wave velocity was 3.6 mm/sec. X-ray diffraction(XRD) on powders crushed from the reacted pellets and microscopicobservation on polished samples showed that the matrix was composed ofdevitrified glass phases, in addition to the TiB₂ phase.

EXAMPLE 15

Reactant powders were dry mixed in proportions corresponding to a matrixcomposition of 50A₂O₃-30CaO-5SiO₂-15BaO for at least 12 hours using ballmilling. Cylindrical pellets of 2.5 grams each were then presseduniaxially to a green density of ˜60% of theoretical. The pellets werethen ignited in a combustion chamber by resistant heating a W-coil underinert Argon atmosphere. The average combustion temperature (Tc) was 1958K and the average wave velocity was 3.2 mm/sec. X-ray diffraction (XRD)on powders crushed from the reacted pellets and microscopic observationon polished samples showed that the matrix was composed of a mixture ofglass and devitrified glass phases, in addition to the TiB₂ phase.

EXAMPLE 16

Reactant powders were dry mixed in proportions corresponding to a matrixcomposition of 50A₂O₃-30CaO-10SiO₂-10BaO for at least 12 hours usingball milling. Cylindrical pellets of 2.5 grams each were then presseduniaxially to a green density of ˜60% of theoretical. The pellets werethen ignited in a combustion chamber by resistant heating a W-coil underinert Argon atmosphere. The average combustion temperature (Tc) was 1912K and the average wave velocity was 2.8 mm/sec. X-ray diffraction (XRD)on powders crushed from the reacted pellets and microscopic observationon polished samples showed that the matrix was composed of pure glassphase, in addition to the TiB₂ phase.

EXAMPLE 17

Reactant powders were dry mixed in proportions corresponding to a matrixcomposition of 50A₂O₃-30CaO-15SiO₂-5BaO for at least 12 hours using ballmilling. Cylindrical pellets of 2.5 grams each were then presseduniaxially to a green density of ˜60% of theoretical. The pellets werethen ignited in a combustion chamber by resistant heating a W-coil underinert Argon atmosphere. The average combustion temperature (Tc) was 1950K and the average wave velocity was 1.6 mm/sec. X-ray diffraction (XRD)on powders crushed from the reacted pellets and microscopic observationon polished samples showed that the matrix was composed of pure glassphase, in addition to the TiB₂ phase.

EXAMPLE 18

Reactant powders were dry mixed in proportions corresponding to a matrixcomposition of 50A₂O₃-30CaO-17.5SiO₂-2.5BaO for at least 12 hours usingball milling. Cylindrical pellets of 2.5 grams each were then presseduniaxially to a green density of ˜60% of theoretical. The pellets werethen ignited in a combustion chamber by resistant heating a W-coil underinert Argon atmosphere. The average combustion temperature (Tc) was 1806K and the average wave velocity was 1.9 mm/sec. X-ray diffraction (XRD)on powders crushed from the reacted pellets and microscopic observationon polished samples showed that the matrix was composed of mainly glassphase with only very slight devitrification, in addition to the TiB₂phase.

EXAMPLE 19

Reactant powders were dry mixed in proportions corresponding to a matrixcomposition of 45A₂O₃-27CaO-20SiO₂-8BaO for at least 12 hours using ballmilling. Cylindrical pellets of 2.5 grams each were then presseduniaxially to a green density of ˜60% of theoretical. The pellets werethen ignited in a combustion chamber by resistant heating a W-coil underinert Argon atmosphere. The average combustion temperature (Tc) was 1916K and the average wave velocity was 2.1 mm/sec. X-ray diffraction (XRD)on powders crushed from the reacted pellets and microscopic observationon polished samples showed that the matrix was composed of pure glassphase, in addition to the TiB₂ phase.

EXAMPLE 20

Reactant powders were dry mixed in proportions corresponding to a matrixcomposition of 41.7A₂O₃-25CaO-20SiO₂-13.3BaO for at least 12 hours usingball milling. Cylindrical pellets of 2.5 grams each were then presseduniaxially to a green density of ˜60% of theoretical. The pellets werethen ignited in a combustion chamber by resistant heating a W-coil underinert Argon atmosphere. The average combustion temperature (Tc) was 1916K and the average wave velocity was 2.1 mm/sec. X-ray diffraction (XRD)on powders crushed from the reacted pellets and microscopic observationon polished samples showed that the matrix was composed of pure glassphase, in addition to the TiB₂ phase. Examples 1-20 used titaniumdioxide (rutile) as one of the reactants (reactions 1-3). The followingexamples used titanium hydride as one of the reactants (reaction 4).

EXAMPLE 21

Reactant powders were dry mixed in proportions corresponding to a matrixcomposition of 50A₂O₃-30CaO-10SiO₂-10BaO for at least 12 hours usingball milling. Cylindrical pellets of 2.5 grams each were then presseduniaxially to a green density of 60% of theoretical. The pellets werethen ignited in a combustion chamber by resistant heating a W-coil underinert Argon atmosphere. The average combustion temperature (Tc) was 1959K and the average wave velocity was 1.8 mm/sec. X-ray diffraction (XRD)on powders crushed from the reacted pellets and microscopic observationon polished samples showed that the matrix was composed of pure glassphase, in addition to the TiB₂ phase. The average apparent porosity was39% as compared to 19% for the same composition samples produced inExample 15.

EXAMPLE 22

Reactant powders were dry mixed in proportions corresponding to a matrixcomposition of 50A₂O₃-30CaO-15SiO₂-5BaO for at least 12 hours using ballmilling. Cylindrical pellets of 2.5 grams each were then presseduniaxially to a green density of ˜60% of theoretical. The pellets werethen ignited in a combustion chamber by resistant heating a W-coil underinert Argon atmosphere. The average combustion temperature (Tc) was 1871K and the average wave velocity was 1.2 mm/sec. X-ray diffraction (XRD)on powders crushed from the reacted pellets and microscopic observationon polished samples showed that the matrix was composed of pure glassphase, in addition to the TiB₂ phase. The average apparent porosity was42% as compared to 11% for the same composition samples produced inExample 16.

The following examples used titanium as one of the reactants (Reaction5).

EXAMPLE 23

Reactant powders were dry mixed in proportions corresponding to a matrixcomposition of 50A₂O₃-30CaO-10SiO₂-10BaO for at least 12 hours usingball milling. Cylindrical pellets of 2.5 grams each were then presseduniaxially to a green density of ˜60% of theoretical. The pellets werethen ignited in a combustion chamber by resistant heating a W-coil underinert Argon atmosphere. The average combustion temperatures (Tc) were2324 K and wave velocities were 5.2 mm/sec. The X-ray diffraction (XRD)on powders crushed from the reacted pellets and microscopic observationon polished samples showed that the matrix was composed of pure glassphase, in addition to the TiB₂ phase.

EXAMPLE 24

Reactant powders were dry mixed in proportions corresponding to a matrixcomposition of 50A₂O₃-30CaO-15SiO₂-5BaO for at least 12 hours using ballmilling. Cylindrical pellets of 2.5 grams each were then presseduniaxially to a green density of ˜60% of theoretical. The pellets werethen ignited in a combustion chamber by resistant heating a W-coil underinert Argon atmosphere. The average combustion temperatures (Tc) were2229 K and wave velocities were 4.8 mm/sec. The X-ray diffraction (XRD)on powders crushed from the reacted pellets and microscopic observationon polished samples showed that the matrix was composed of pure glassphase, in addition to the TiB₂ phase.

EXAMPLE 25

Reactant powders were dry mixed in proportions corresponding to a matrixcomposition of 50A₂O₃-30CaO-17.5SiO₂-2.5BaO for at least 12 hours usingball milling. Cylindrical pellets of 2.5 grams each were then presseduniaxially to a green density of ˜60% of theoretical. The pellets werethen ignited in a combustion chamber by resistant heating a W-coil underinert Argon atmosphere. The average combustion temperatures (Tc) were2258 K and wave velocities were 5.2 mm/sec. The X-ray diffraction (XRD)on powders crushed from the reacted pellets and microscopic observationon polished samples showed that the matrix was composed of pure glassphase, in addition to the TiB₂ phase.

Combustion synthesis of glass (Al₂O₃—CaO—X) ceramic (TiB₂) compositeshas been described with reference to particular embodiments. Othermodifications and enhancements can be made without departing from thespirit and scope of the claims that follow.

What is claimed is:
 1. A process of making a glass-ceramic compositecomprising the steps of: a. providing powdered T, B₂O₃, Al, CaO, X andY, where T, X and Y are different, T is selected from the groupconsisting of Ti, TiO₂ and TiH₂, X is selected from the group consistingof metal and metal oxide and Y is selected from the group consisting ofmetal and metal oxide; b. weighing the powders in the following moleratio: 3TiO₂, 3B₂O₃,10Al, αCaO, βX and γY if T is TiO₂ and T, B₂O₃, 2Al,αCaO, βX and γY if T is selected from the group consisting of Ti andTiH₂, where α, β and γ represent non-zero numbers; c. mixing the powdersdry for adequate time in a ball mill; d. forming the mixed powders intoa green pellet, uniaxially, to a density of about 60% theoretical; ande. igniting the pellet, whereby a reaction product having the formula3TiB₂-5Al₂O₃-αCaO-βX-γY is produced if T is TiO₂ and a reaction producthaving the formula TiB₂-Al₂O₃-αCaO-βX-γY is produced if T is selectedfrom the group consisting of Ti and TiH₂.
 2. A process of making aglass-ceramic composite as claimed in claim 1 in which the BaO powderhas a particle sizes less than 44 μm and contains impurities less than0.5% and all other powders have a particle size of less than 44 μm andcontain impurities less than 1%.
 3. A process of making a glass-ceramiccomposite as claimed in claim 1 in which ignition is performed byresistance heating a W coil in an inert atmosphere inside a reactionchamber.
 4. A process of making a glass-ceramic composite as claimed inclaim 1 in which ignition is performed by resistance heating aKanthal-wire in air.
 5. A process of making a glass-ceramic composite asclaimed in claim 1 in which ignition is performed by burning of aregular torch in air.
 6. A process of making a glass-ceramic compositeas claimed in claim 1 in which ignition is performed by placing thepellets into a furnace previously heated to over 600° C.
 7. A process ofmaking a glass-ceramic composite as claimed in claim 1 in which X isSiO₂ and Y is BaO.
 8. A process of making a glass-ceramic compositecomprising the steps of: a. providing powdered TiO₂, B₂O₃, Al and CaO;b. weighing the powders in the following mole ratio: 3TiO₂, 3B₂O₃, 10Al,αCaO where α represents a non-zero number; c. mixing the powders dry foradequate time in a ball mill; d. forming the mixed powders into a greenpellet, uniaxially, to a density of about 60% theoretical; and e.igniting the pellet, whereby a reaction product having the formula3TiB2-5Al₂O₃-αCaO is produced.
 9. A process of making a glass-ceramiccomposite as claimed in claim 8 in which the powders have particle sizesless than 44 μm and contain less than 1% impurities.
 10. A process ofmaking a glass-ceramic composite as claimed in claim 8 in which ignitionis performed by resistance heating a W coil in an inert atmosphereinside a reaction chamber.
 11. A process of making a glass-ceramiccomposite as claimed in claim 8 in which ignition is performed byresistance heating a Kanthal-wire in air.
 12. A process of making aglass-ceramic composite as claimed in claim 8 in which ignition isperformed by burning of a regular torch in air.
 13. A process of makinga glass-ceramic composite as claimed in claim 8 in which ignition isperformed by placing the pellets into a furnace previously heated toover 600° C.
 14. A process of making a glass-ceramic composite asclaimed in claim 8 further comprising the steps of: a. providingpowdered X, which is selected from the group consisting of any metal andany metal oxide except TiO₂; and b. adding βX to the other powders priorto mixing; whereby said reaction product additionally contains βX.
 15. Aprocess of making a glass-ceramic composite comprising the steps of: a.providing powdered TiO₂, B₂O₃, Al, CaO and X, where X is selected fromthe group consisting of any metal and any metal oxide except TiO₂; b.weighing the powders in the following mole ratio: 3TiO₂, 3B₂O₃, 10Al,αCaO, βX, where α and β represent non-zero numbers; c. mixing thepowders dry for adequate time in a ball mill; d. forming the mixedpowders into a green pellet, uniaxially, to a density of about 60%theoretical; and e. igniting the pellet, whereby a reaction producthaving the formula 3TiB₂-5Al₂O₃-αCaO-βX is produced.
 16. A process ofmaking a glass-ceramic composite as claimed in claim 15 in which thepowders have particle sizes less than 44 μm and contain less than 1%impurities.
 17. A process of making a glass-ceramic composite as claimedin claim 15 in which ignition is performed by resistance heating a Wcoil in an inert atmosphere inside a reaction chamber.
 18. A process ofmaking a glass-ceramic composite as claimed in claim 15 in whichignition is performed by resistance heating a Kanthal-wire in air.
 19. Aprocess of making a glass-ceramic composite as claimed in claim 15 inwhich ignition is performed by burning of a regular torch in air.
 20. Aprocess of making a glass-ceramic composite as claimed in claim 15 inwhich ignition is performed by placing the pellets into a furnacepreviously heated to over 600° C.
 21. A process of making aglass-ceramic composite as claimed in claim 15 in which X is selectedfrom the group consisting of SiO₂ and BaO.